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BTU per Hour to Milliwatt Converter

Convert BTU/h to milliwatts with our free online power converter.

Quick Answer

1 BTU per Hour = 293.07107 milliwatts

Formula: BTU per Hour × conversion factor = Milliwatt

Use the calculator below for instant, accurate conversions.

Our Accuracy Guarantee

All conversion formulas on UnitsConverter.io have been verified against NIST (National Institute of Standards and Technology) guidelines and international SI standards. Our calculations are accurate to 10 decimal places for standard conversions and use arbitrary precision arithmetic for astronomical units.

Last verified: February 2026Reviewed by: Sam Mathew, Software Engineer

BTU per Hour to Milliwatt Calculator

How to Use the BTU per Hour to Milliwatt Calculator:

  1. Enter the value you want to convert in the 'From' field (BTU per Hour).
  2. The converted value in Milliwatt will appear automatically in the 'To' field.
  3. Use the dropdown menus to select different units within the Power category.
  4. Click the swap button (⇌) to reverse the conversion direction.
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How to Convert BTU per Hour to Milliwatt: Step-by-Step Guide

Converting BTU per Hour to Milliwatt involves multiplying the value by a specific conversion factor, as shown in the formula below.

Formula:

mW = BTU/h × 293.071

Example Calculation:

1 BTU/h = 293.07107 mW

Disclaimer: For Reference Only

These conversion results are provided for informational purposes only. While we strive for accuracy, we make no guarantees regarding the precision of these results, especially for conversions involving extremely large or small numbers which may be subject to the inherent limitations of standard computer floating-point arithmetic.

Not for professional use. Results should be verified before use in any critical application. View our Terms of Service for more information.

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What is a BTU per Hour and a Milliwatt?

1 BTU/h = 0.293 W = 0.000293 kW

Key equivalents:

  • 3,412 BTU/h = 1 kW
  • 12,000 BTU/h = 1 ton of refrigeration = 3.52 kW
  • 1 BTU/h = 0.2931 W

1 mW = 0.001 W = 0.000001 kW = 1,000 µW (microwatts)

Note: The BTU per Hour is part of the imperial/US customary system, primarily used in the US, UK, and Canada for everyday measurements. The Milliwatt belongs to the imperial/US customary system.

Common Uses and Applications: BTU/h vs milliwatts

Explore the typical applications for both BTU per Hour (imperial/US) and Milliwatt (imperial/US) to understand their common contexts.

Common Uses for BTU/h

Air Conditioning: Window units (5,000-18,000 BTU/h), central systems (18,000-60,000 BTU/h). Furnaces: Home heating (40,000-150,000 BTU/h input). Water Heaters: Gas water heaters (30,000-50,000 BTU/h). HVAC Design: Load calculations, equipment sizing, ductwork design.

When to Use milliwatts

Lasers: Pointer lasers (1-5 mW), barcode scanners (1-10 mW). Wireless: Bluetooth (1-100 mW), Wi-Fi (10-1,000 mW), RFID tags. Medical: Hearing aids (1 mW), pacemakers (50-100 µW standby). Electronics: LEDs, sensors, low-power circuits.

Additional Unit Information

About BTU per Hour (BTU/h)

How many BTU/h do I need for air conditioning?

Basic calculation: Room square footage × 20-25 BTU/h

Adjustments:

  • Sunny room: Add 10%
  • Shaded room: Subtract 10%
  • Kitchen: Add 4,000 BTU/h
  • More than 2 people: Add 600 BTU/h per person
  • High ceilings (>8 ft): Add 10-20%

Examples:

  • 200 sq ft bedroom: 4,000-5,000 BTU/h (5,000 BTU window unit)
  • 400 sq ft living room: 8,000-10,000 BTU/h (10,000 BTU window unit)
  • 1,500 sq ft home: 30,000-36,000 BTU/h (2.5-3 ton central AC)

[BTU/h calculator for HVAC sizing]

How do I convert BTU/h to watts or kW?

Formula:

  • Watts = BTU/h × 0.293
  • kW = BTU/h ÷ 3,412

Examples:

  • 12,000 BTU/h = 3,517 W = 3.52 kW (1 ton AC)
  • 24,000 BTU/h = 7,034 W = 7.03 kW (2 ton AC)
  • 10,000 BTU/h = 2,930 W = 2.93 kW (window unit)
  • 1,000 BTU/h = 293 W

BTU/h to Watts converter → BTU/h to kW converter →

What is the difference between BTU and BTU/h?

BTU = Energy (total heat/cooling) BTU/h = Power (rate of heating/cooling)

Analogy:

  • BTU = distance traveled (miles)
  • BTU/h = speed (miles per hour)

Example:

  • A 10,000 BTU/h air conditioner removes 10,000 BTU of heat per hour
  • Running for 3 hours removes 30,000 BTU total

Always use BTU/h when rating HVAC equipment capacity!

How many BTU/h equals 1 ton of refrigeration?

1 ton = 12,000 BTU/h = 3.52 kW

Origin: Based on melting 1 ton (2,000 lbs) of ice in 24 hours

Common AC sizes:

  • 1 ton = 12,000 BTU/h (small rooms, ~400-600 sq ft)
  • 1.5 tons = 18,000 BTU/h (larger rooms, ~600-900 sq ft)
  • 2 tons = 24,000 BTU/h (small homes, ~900-1,200 sq ft)
  • 2.5 tons = 30,000 BTU/h (medium homes, ~1,200-1,500 sq ft)
  • 3 tons = 36,000 BTU/h (larger homes, ~1,500-1,800 sq ft)
  • 4 tons = 48,000 BTU/h (large homes, ~2,000-2,400 sq ft)
  • 5 tons = 60,000 BTU/h (very large homes, ~2,400-3,000 sq ft)

BTU/h to Tons converter →

How efficient is my furnace or AC?

Furnace efficiency (AFUE):

  • Old furnace: 60-70% AFUE
  • Standard: 80% AFUE (80,000 BTU/h input → 64,000 BTU/h heat output)
  • High-efficiency: 90-98% AFUE

AC efficiency (SEER):

  • Old AC: SEER 8-10 (inefficient)
  • Standard: SEER 13-14 (minimum new units)
  • High-efficiency: SEER 16-20
  • Ultra-high: SEER 20-26

EER (Energy Efficiency Ratio) = BTU/h output ÷ watts input

  • Good window AC: EER 10-12
  • Excellent: EER 12+

About Milliwatt (mW)

How do I convert mW to watts or microwatts?

Formula:

  • W = mW × 0.001 (or mW ÷ 1,000)
  • µW = mW × 1,000

Examples:

  • 1 mW = 0.001 W = 1,000 µW
  • 100 mW = 0.1 W = 100,000 µW
  • 1,000 mW = 1 W = 1,000,000 µW
  • 10 mW = 0.01 W = 10,000 µW

mW to Watts converter →

What is a safe laser power in mW?

Laser safety classes:

Class 1 (< 0.4 mW): Inherently safe, cannot damage eye Class 2 (0.4-1 mW): Safe with blink reflex (~0.25 seconds) Class 3R (1-5 mW): Low risk with brief exposure, common laser pointers Class 3B (5-500 mW): Eye hazard, can cause injury Class 4 (> 500 mW): Severe eye and skin hazard, fire risk

Recommendations:

  • Safe for general use: ≤ 1 mW (Class 2)
  • Laser pointers (legal): < 5 mW in US (many countries limit to 1 mW)
  • Avoid: > 5 mW for general use
  • Industrial/medical: 10-10,000+ mW (requires safety training)

Example: 5 mW green laser appears ~30x brighter than 5 mW red laser to human eye (wavelength sensitivity).

How much power does a typical Bluetooth device use?

Bluetooth power classes:

Class 1: 100 mW (20 dBm) - Range: ~100 meters

  • Use case: Industrial, long-range applications

Class 2: 2.5 mW (4 dBm) - Range: ~10 meters

  • Use case: Most consumer devices (headphones, mice)

Class 3: 1 mW (0 dBm) - Range: ~1 meter

  • Use case: Very low power, proximity devices

Bluetooth Low Energy (BLE): 0.01-10 mW

  • Advertising: 0.01-1 mW (intermittent)
  • Connected: 1-10 mW
  • Deep sleep: 0.001-0.01 mW

Examples:

  • Wireless earbuds: 2-10 mW (Class 2/3)
  • Bluetooth speaker: 2.5-10 mW (Class 2)
  • Fitness tracker: 0.1-5 mW (BLE)

What is dBm and how does it relate to mW?

dBm = Decibels relative to 1 milliwatt (logarithmic power scale)

Formula: dBm = 10 × log₁₀(mW)

Common conversions:

| dBm | mW | Description | |-----|-------|-------------| | 0 | 1 | Reference | | 3 | 2 | Double | | 10 | 10 | 10x | | 20 | 100 | 100x | | 30 | 1,000 | 1W | | -10 | 0.1 | 1/10 | | -20 | 0.01 | 1/100 | | -30 | 0.001 | 1 µW |

Why use dBm?

  • Large ranges easier to express: -50 dBm to +30 dBm vs 0.00001 mW to 1,000 mW
  • Simplifies gain/loss calculations (add/subtract vs multiply/divide)

Examples:

  • Wi-Fi signal: -30 to -90 dBm (1,000 mW to 0.000001 mW)
  • Cell tower: +43 dBm = 20,000 mW (20W)
  • Bluetooth: 0 to +20 dBm (1-100 mW)

How long can a battery power a device using mW?

Formula: Battery life (hours) = (Battery capacity in mWh) ÷ (Device power in mW)

Example calculations:

CR2032 coin cell: 225 mAh @ 3V = 675 mWh

  • LED (20 mW): 675 ÷ 20 = 34 hours
  • Bluetooth beacon (1 mW avg): 675 ÷ 1 = 675 hours (~28 days)
  • Watch (0.01 mW avg): 675 ÷ 0.01 = 67,500 hours (~7.7 years)

AA battery: 2,500 mAh @ 1.5V = 3,750 mWh

  • LED flashlight (500 mW): 3,750 ÷ 500 = 7.5 hours
  • Remote control (5 mW avg): 3,750 ÷ 5 = 750 hours (~31 days active)

Smartphone battery: 15 Wh = 15,000 mWh

  • Idle (200 mW): 15,000 ÷ 200 = 75 hours (~3 days)
  • Active use (2,000 mW): 15,000 ÷ 2,000 = 7.5 hours

Conversion Table: BTU per Hour to Milliwatt

BTU per Hour (BTU/h)Milliwatt (mW)
0.5146.536
1293.071
1.5439.607
2586.142
51,465.355
102,930.711
257,326.777
5014,653.554
10029,307.107
25073,267.768
500146,535.535
1,000293,071.07

People Also Ask

How do I convert BTU per Hour to Milliwatt?

To convert BTU per Hour to Milliwatt, enter the value in BTU per Hour in the calculator above. The conversion will happen automatically. Use our free online converter for instant and accurate results. You can also visit our power converter page to convert between other units in this category.

Learn more →

What is the conversion factor from BTU per Hour to Milliwatt?

The conversion factor depends on the specific relationship between BTU per Hour and Milliwatt. You can find the exact conversion formula and factor on this page. Our calculator handles all calculations automatically. See the conversion table above for common values.

Can I convert Milliwatt back to BTU per Hour?

Yes! You can easily convert Milliwatt back to BTU per Hour by using the swap button (⇌) in the calculator above, or by visiting our Milliwatt to BTU per Hour converter page. You can also explore other power conversions on our category page.

Learn more →

What are common uses for BTU per Hour and Milliwatt?

BTU per Hour and Milliwatt are both standard units used in power measurements. They are commonly used in various applications including engineering, construction, cooking, and scientific research. Browse our power converter for more conversion options.

For more power conversion questions, visit our FAQ page or explore our conversion guides.

Helpful Conversion Guides

Learn more about unit conversion with our comprehensive guides:

📚 How to Convert Units

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🔢 Conversion Formulas

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⚖️ Metric vs Imperial

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⚠️ Common Mistakes

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View All Guides →

All Power Conversions

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Verified Against Authority Standards

All conversion formulas have been verified against international standards and authoritative sources to ensure maximum accuracy and reliability.

NIST Reference on Constants, Units and Uncertainty

National Institute of Standards and Technology — Fundamental physical constants and unit conversions

BIPM SI Units

Bureau International des Poids et Mesures — International System of Units (SI) definitions and standards

ISO 80000

International Organization for Standardization — Quantities and units international standards series

Last verified: February 19, 2026